Systems and methods for determining ventricular pacing sites for use with multi-pole leads

ABSTRACT

Techniques are provided for use by implantable medical devices for controlling multi-site left ventricular (MSLV) pacing using a multi-pole left ventricular (LV) lead. In various examples, a reduced number of “V sense”, “RV pace”, and “LV pace” tests are performed to determine preferred or optimal interventricular pacing delays (VV) for use with MSLV pacing. Additionally, techniques are described for sorting the order by which LV sites are to be paced during MSLV pacing. Furthermore, techniques are described for detecting and addressing circumstances where AV/PV delays are longer than corresponding AR/PR delays during MSLV.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. patentapplication Ser. No. 12/507,646, of Min, filed Jul. 22, 2009, entitled“Systems and Methods for Optimizing Ventricular Pacing Delays for usewith Multi-Pole Leads,” which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention generally relates to implantable cardiac stimulationdevices such as pacemakers and implantable cardioverter-defibrillators(ICDs) and, in particular, to techniques for determining preferred oroptimal multi-site interventricular (VV) pacing delays for use in pacingthe ventricles using multi-pole left ventricular leads.

BACKGROUND OF THE INVENTION

Clinical studies related to cardiac pacing have shown that an optimalatrio-ventricular pacing delay (e.g., AV delay or PV delay) and/or anoptimal interventricular pacing delay (e.g., VV delay) can improvecardiac performance. However, such optimal delays depend on a variety offactors that may vary over time. Thus, what is “optimal” may vary overtime. An optimization of AV/PV pacing delay and/or VV pacing delay maybe performed at implantation and sometimes, a re-optimization may beperformed during a follow-up consultation. While such optimizations arebeneficial, the benefits may not last due to changes in various factorsrelated to device and/or cardiac function.

The following patents and patent applications set forth various systemsand methods for allowing a pacemaker, implantablecardioverter-defibrillator (ICD) or other cardiac rhythm management(CRM) device to determine and/or adjust AV/PV/VV pacing delays so as tohelp maintain the pacing delays at optimal values: U.S. patentapplication Ser. No. 10/703,070, filed Nov. 5, 2003, entitled “Methodsfor Ventricular Pacing” (Attorney Docket No. A03P1074), now abandoned;U.S. patent application Ser. No. 10/974,123, filed Oct. 26, 2004(Attorney Docket No. A03P1074US01), now abandoned; U.S. patentapplication Ser. No. 10/986,273, filed Nov. 10, 2004, now U.S. Pat. No.7,590,446 (Attorney Docket No. A03P1074US02); U.S. patent applicationSer. No. 10/980,140, filed Nov. 1, 2004 (Attorney Docket No.A03P1074US03), now abandoned; U.S. patent application Ser. No.11/129,540, filed May 13, 2005 (Attorney Docket No. A03P1074US04); andU.S. patent application Ser. No. 11/952,743, filed Dec. 7, 2007(Attorney Docket No. A07P1179). See, also, U.S. patent application Ser.No. 12/328,605, filed Dec. 4, 2008, entitled “Systems and Methods forControlling Ventricular Pacing in Patients with Long Intra-AtrialConduction Delays” (Attorney Docket No. A08P1067) and U.S. patentapplication Ser. No. 12/132,563, filed Jun. 3, 2008, entitled “Systemsand Methods for determining Intra-Atrial Conduction Delays usingMulti-Pole Left Ventricular Pacing/Sensing Leads” (Attorney Docket No.A08P1021). See, further, U.S. Pat. No. 7,248,925, to Bruhns et al.,entitled “System and Method for Determining Optimal AtrioventricularDelay based on Intrinsic Conduction Delays.” At least some of thetechniques are implemented within the QuickOpt™ systems of St. JudeMedical.

In particular, techniques were set forth within at least some of thesepatent documents for exploiting various inter-atrial andinterventricular conduction delays to determine preferred or optimalAV/PV/VV pacing delays. Techniques were also set forth for exploitingthe VV delays to determine which ventricles should be paced—the leftventricle (LV), the right ventricle (RV), both ventricles, or neither,and in which order. In at least some examples, the implanted device (oran external programming device in communication with the implanteddevice) performs a series of tests to determine intrinsic AV/PV and VVconduction delays from which preferred pacing delays are determined. Inparticular, an “A sense” test is performed to detect intrinsicintra-atrial delays from which preferred AV/PV pacing delays aredetermined. A “V sense” test is performed to detect intrinsicventricular events from which an intrinsic interventricular conductiondelay (Δ) is determined. An “RV pace” test and a separate “LV pace” testare performed to detect paced interventricular conduction delays(IVCD_RL and IVCD_LR, respectively) from which an intrinsicinterventricular correction term (ε) is determined. The optimal VV delayfor use in biventricular pacing is then set based on Δ and ε.

Issues can arise, though, when using a multi-pole LV lead for multi-siteLV (MSLV) pacing. With a multi-pole LV lead—rather than having only apair of tip and ring electrodes at a distal end of the lead—numerouselectrodes are provided along the lead so that pacing/sensing can beperformed at any of a variety of selected locations on or in the LV.With a multi-pole lead, the number of tests to be performed to optimizepacing delays can become numerous and time consuming. Typically, aseparate V sense test would be employed for each of the LV electrodes(in combination with a particular RV electrode.) So, for example, for aquadra-pole LV lead, four V sense tests would be performed, one for eachof the four electrodes of the LV lead. Likewise, typically, separate RVand LV pace tests would be employed for each of the LV electrodes (incombination with the RV electrode.) Again, for the example of aquadra-pole LV lead, four RV pace tests would be performed, one for eachof the four electrodes of the LV lead. As such, the overall test timefor optimizing VV pacing parameters for a multi-pole LV lead might besignificant, with resulting costs and inconveniences to patient andclinician.

Accordingly, the invention is generally directed to providing improvedtest techniques for use with multi-pole leads to allow for more promptand efficient determination of preferred or optimal VV pacing delays.Some aspects of the invention are directed to identifying the order bywhich a set of MSLV pacing pulses are to be delivered to various siteswithin the LV (i.e. to determine which LV site is to be paced first,which site is to be paced second, and so on.) Still other aspects aredirected to addressing circumstances where the PV pacing delays to beused are longer than intrinsic PR delays or where the AV pacing delaysto be used are longer than intrinsic AR delays.

SUMMARY OF THE INVENTION

In an exemplary embodiment, a method is provided for controlling thedelivery of cardiac pacing therapy by an implantable cardiac rhythmmanagement device equipped with a multi-pole ventricular lead having aplurality of electrodes. Briefly, preliminary multi-siteinterventricular pacing delays (VVT) are determined for the plurality ofelectrodes of the multi-pole lead based, at least in part, on multi-siteinterventricular conduction time delay values (Δ) determined for theelectrodes. Multi-site interelectrode pacing delays (IVV) are determinedfor the plurality of electrodes of the multi-pole lead based thepreliminary interventricular pacing delays (VVT). The order by which theelectrodes of the multi-pole lead are to be used to deliver a set ofmulti-site pacing pulses is then determined, with the order set based onthe interelectrode pacing time delays (IVV). A set of multi-site pacingpulses is then delivered using the electrodes of the multi-pole lead inthe sorted order.

In an illustrative example, the implantable device is a pacemaker, ICDor cardiac resynchronization therapy (CRT) device equipped with amulti-pole LV lead having a plurality of individual LV electrodes(LV_(n)). The device is also equipped with an RV lead having at leastone RV electrode. The overall method is performed to control MSLV pacingdelivered using some combination of RV and LV electrodes. In oneparticular example, the LV lead has four electrodes—a tip electrode andthree ring electrodes arrange sequentially along the lead adjacent theLV. Herein, the four electrodes of the quadrapole example are denotedn=1, 2, . . . , N where N=4. That is, the first or tip electrode isdenoted n=1. The first ring electrode is denoted n=2, and so on.

In a quadra-pole example, the multi-site interventricular pacing timedelays are determined by determining a preliminary interventricularpacing delay (VV_(n)) for use with a selected electrode (LV_(n)) of theLV lead based on:

VVT _(n)=α*(Δ′_(n)+ε_(n)); wherein n=1, 2, 3, 4

wherein α_(n) is 0.5 (or other suitable coefficient), Δ′_(n) is anintrinsic interelectrode conduction time delay obtained within thepatient, and ε_(n) is an interventricular correction term for use withthe selected electrode (LV_(n)) of the LV lead.

In the quadra-pole example, the interelectrode conduction time delay(Δ′_(n)) can be determined using:

Δ′_(n)=Δ_(n)−Δ_(n−1); where n=2, 3, . . . , N

Δ′₁=Δ₁

wherein Δ_(n) is a measured intrinsic interventricular conduction timedelay for the nth electrode of the multi-pole lead, which is measuredwithin the patient based on intrinsic depolarization events, such asduring a V-sense test. In the quadrapole example, the interventricularcorrection term (ε_(n)) is determined based on:

ε_(n)=IVCD(L _(n) L _(n−1))−IVCD(L _(n−1) L _(n)) where n=2, 3, . . . ,N

ε₁=IVCD(L ₁ R)−IVCD(RL ₁)

wherein IVCD represents the paced interventricular conduction time delay(IVCD) for various pairs of electrodes of the system as determined usingRV pace and LV pace tests and N is the number of electrodes.

In the quadra-pole example, the order by which LV sites are to be pacedis determined by: selectively summing values of VVT_(n) to generatevalues for the interelectrode pacing delays (IVV_(n)); determiningabsolute values of each of the IVV_(n) values; identifying the IVV_(n)value having the maximum absolute value and selecting the correspondingelectrode (n) as being the first electrode to be paced; and thenrepeating the process with the remaining IVV_(n) values and theremaining electrodes to iteratively sort the IVV_(n) values and thecorresponding electrodes.

In one particular quadra-pole embodiment, the device calculates the setof IVV_(n) values using:

Sum=0

IVV(0)=0 (for RV electrode)

For i=1 to 4

-   -   Sum=Sum+VVT(i);    -   IVV(i)=Sum;

End loop.

The device then assesses the relative absolute values of the IVV valuesto sort the order the LV pacing sites. The device also determines finalinterventricular pacing delays (VV_(n)) for use with each of theelectrodes of the LV lead based on differences between IVV_(n) values ofthe electrodes. In an illustrative example, the order with whichstimulation pulses are to be delivered to the four electrodes of the LVlead is determined to be: 3rd electrode, 1st electrode, 2nd electrodeand 4th electrode, with the RV electrode paced last. That is, the sortedorder is: IVV(3), IVV(1), IVV(2), IVV(4), RV=0. In that example, the VVdelay applied at the 3rd electrode (VV₃) is IVV(3); the VV delay appliedat the 1st electrode (VV₁) is IVV(3)-IVV(1); the VV delay applied at the2nd electrode (VV₂) electrode is IVV(1)-IVV(2); the VV delay applied atthe 4th electrode (VV₄) electrode is IVV(2)-IVV(4); and the delayapplied to the RV electrode is IVV(4)-0.

Also, in the exemplary embodiment, steps are taken to addresscircumstances where PV pacing delays to be used are longer thanintrinsic PR delays or where the AV pacing delays to be used are longerthan intrinsic AR delays (i.e. where the PV/AV values are too longresulting in intrinsic ventricular depolarization before paceddepolarization.) In one particular example, A sense and A pace tests areperformed. In the A sense test, the device measures an intrinsicatrioventricular time delay (PR_(RV)) between a P-wave and an RV QRS andthen determines an intrinsic atrioventricular time delay (PR_(LVn))between the P-wave and each of the plurality of LV electrodes. In the Apace test, the device measures an atrioventricular time delay (AR_(RV))between an initial A-pulse and an RV QRS and then determines a pacedatrioventricular time delay (AR_(LVn)) between the initial A-pulse andeach of the plurality of LV electrodes. The device determines whetherthe resulting PV values exceed corresponding PR value and if so, LVpacing is delivered using two or more other electrodes where PV does notexceed the corresponding PR. For example, LV pacing sites are identifiedwhere PV+VV_(n)<PR(L_(n)) and then pacing is delivered at those siteswithout pacing the RV. Similar considerations apply to circumstanceswhere AV exceeds the corresponding AR value.

Although described primarily with respect to implementations having amulti-pole LV electrode, aspects of the invention are also applicable,where appropriate, to multi-pole RV leads or multi-pole atrial leads aswell. In general, techniques are provided herein to determineinterchamber conduction delays (such as a paced interchamber conductiontime delay and an intrinsic interchamber conduction time delay) forsetting interchamber pacing delays and for determining the order atwhich stimulation is delivered among multi-sites within a given chamber.Note also that, herein, by “interventricular”, it is meant that thedelays are between different sites within the ventricles.Interventricular delays can broadly include, e.g., delays between LVsites and RV sites, as well as delays between different LV sites. Delaysbetween different LV sites can also be referred to as LV“intraventricular” delays or LV “interelectrode” delays.

System and method implementations of various exemplary techniques arepresented herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the described implementations can be morereadily understood by reference to the following description taken inconjunction with the accompanying drawings.

FIG. 1 illustrates pertinent components of an implantable medical systemhaving a pacemaker or ICD capable of optimizing ventricular pacingdelays for use with a multi-pole LV lead;

FIG. 2 is a flowchart providing an overview of a technique forcontrolling ventricular pacing using a multi-pole LV lead, which may beperformed by the system of FIG. 1;

FIG. 3 is a flowchart illustrating an exemplary biventricularimplementation of the technique of FIG. 2 wherein V sense, RV pace andLV pace tests are used to determine optimal biventricular pacing delays;

FIG. 4 is a graph illustrating an exemplary A-IEGM, RV-IEGM and set ofLVn-IEGMs during V sense tests, and particularly illustrating Δ_(n)intervals exploited by the techniques of FIGS. 2-3;

FIG. 5 is a flowchart exemplary techniques for performing RV pace and LVpace tests for use with the method of FIG. 3;

FIG. 6 is a graph illustrating an RV IEGM and a set of LVn IEGMs sensedduring the RV pace test for use with the method FIG. 5;

FIG. 7 includes several graphs illustrating various RV IEGMs and LVnIEGMs sensed during a set of LV pace tests for use with the method FIG.5;

FIG. 8 is a simplified, partly cutaway view, illustrating the pacer/ICDof FIG. 1 along with at set of leads implanted into the heart of thepatient;

FIG. 9 is a functional block diagram of the pacer/ICD of FIG. 8,illustrating basic circuit elements that provide cardioversion,defibrillation and/or pacing stimulation in the heart an particularlyillustrating an on-board optimization system for performing theoptimization techniques of FIGS. 2-7;

FIG. 10 is a functional block diagram illustrating components of theexternal device programmer of FIG. 1 and particularly illustratingprogrammer-based optimization systems for controlling the optimizationtechniques of FIGS. 2-7;

FIG. 11 is a flowchart providing an overview of an alternative techniquefor controlling ventricular pacing using a multi-pole LV lead, which maybe performed by the system of FIG. 1 wherein steps are taken todetermine the order by which a set of multi-site pacing pulses are to bedelivered to various sites within the ventricles;

FIG. 12 is a flowchart illustrating an exemplary biventricularimplementation of the technique of FIG. 11 wherein V sense, RV pace andLV pace tests are used to determine optimal interventricular pacingdelays and wherein circumstances are addressed where PV pacing delays tobe used are longer than intrinsic PR delays or where AV pacing delays tobe used are longer than intrinsic AR delays;

FIG. 13 is a graph illustrating exemplary LV_(n)-IEGMs during one of aset of four LV pace tests exploited during the technique of FIG. 12; and

FIG. 14 is a flowchart illustrating a method for use with the techniqueof FIG. 12 for determining the order by which LV sites are to be pacedand for determining VV_(n) values.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description includes the best mode presently contemplatedfor practicing the invention. This description is not to be taken in alimiting sense but is made merely to describe general principles of theinvention. The scope of the invention should be ascertained withreference to the issued claims. In the description of the invention thatfollows, like numerals or reference designators will be used to refer tolike parts or elements throughout.

Overview of Implantable System

FIG. 1 illustrates an implantable medical system 8 capable of performingrapid optimization of ventricular pacing parameters using a multi-polelead. The medical system 8 includes a pacer/ICD 10 or other cardiacrhythm management device equipped with one or more cardiacsensing/pacing leads 12 implanted on or within the heart of the patient,including a multi-pole LV lead implanted via the coronary sinus (CS). InFIG. 1, a stylized representation of the set of leads is provided. Toillustrate the multi-pole configuration of the LV lead, a set ofelectrodes 13 is shown distributed along the LV lead. The RV and RAleads are each shown with a single electrode, though each of those leadsmay include additional electrodes as well, such as tip/ring electrodepairs. Still further, the LV lead can also include one or more leftatrial (LA) electrodes mounted on or in the LA via the CS. See FIG. 8for a more complete and accurate illustration of various exemplaryleads.

In some implementations, the pacer/ICD itself performs the multi-poleoptimization based on electrocardiac signals sensed using the leads. Inother implementations, the device transmits features of theelectrocardiac signals to an external device programmer 14 that performsthe optimization. That is, the device programmer determines optimalmulti-pole ventricular pacing parameters, which are then programmed intothe pacer/ICD via telemetry. Other external devices might instead beused to perform the optimization, such as bedside monitors or the like.In some embodiments, the device programmer or bedside monitor isdirectly networked with a centralized computing system, such as theHouseCall™ system or the Merlin@home/Merlin.Net systems of St. JudeMedical.

In the following examples, it is assumed that the pacer/ICD performs themulti-pole optimization using on-board components. An example where theexternal programmer performs the optimization is described below withreference to FIG. 10. FIGS. 2-7 illustrate a first set of exemplarytechniques for multi-pole optimization, also described in theaforementioned parent patent application. FIGS. 11-14 illustrate asecond set of exemplary techniques wherein the order by which LV sitesare to be paced are sorted and wherein circumstances are identified andaddressed where PV/AV delays are longer than corresponding PR/AR delays.

Multi-Pole LV Pacing Optimization

FIG. 2 broadly summarizes a general technique for controllingventricular pacing parameters for use with a multi-pole ventricular leadthat may be exploited by the pacer/ICD of FIG. 1 or other suitablyequipped systems. Beginning at step 100, the pacer/ICD identifies anelectrical event (such as a P-wave or an A-pulse) sufficient to triggerventricular depolarization within the heart of the patient in which thedevice is implanted. At step 102, the pacer/ICD detects a resultingventricular depolarization (QRS complex) at each of a plurality ofelectrodes of the multi-pole lead, the depolarization being detected atgenerally different times at each different electrode. In the examplesdescribed herein, the multi-pole lead is an LV lead, but it should beunderstood that the general techniques of the invention are applicableto multi-pole RV leads. Indeed, the techniques are applicable toimplementations wherein both the LV and RV have multi-pole leads. Stillfurther, the techniques are also generally applicable to multi-poleatrial leads, implanted on or in either the RA or the LA. As such, atleast some of the techniques described herein are generally applicableto optimizing various interchamber pacing delays.

At step 104, the pacer/ICD determines an interventricular conductiontime delay for each of the plurality of electrodes of the multi-polelead based on the depolarization triggered by the electrical event. Theconduction time delay is a paced interventricular conduction time delay(IVCD) and/or an intrinsic interventricular conduction time delay (Δ).At step 106, VV pacing delays for use in controlling ventricular pacingusing a selected electrode of the multi-pole lead can then bedetermined, at least in part, on the conduction time delay determinedfor the selected electrode. Alternatively, monoventricular pacing can becontrolled by using the sign of VV from conduction time delay todetermine the chamber to receive the monoventricular pacing pulses (i.e.RV vs. LV.)

FIG. 3 provides a more detailed example wherein biventricular pacing iscontrolled for use with a multi-pole LV lead having N electrodes(individually denoted LVn). Beginning at step 200, the pacer/ICDperforms a single V sense test. During the V sense test, the pacer/ICD:detects P-waves on an A-IEGM channel sensed using an RA lead and/ordelivers A-pulse to the RA using the RA lead. The P-waves may bedetected during a contemporaneous A sense test. The A-pulses may bedelivered during a contemporaneous A pulse test. That is, the V sensetest may be performed at the same time as A sense/A pace tests toenhance overall test efficiency. See the patent documents cited abovefor discussions of A sense/A pace tests, which are generally used todetermine intra-atrial (AE/PE) delays for use in settingatrioventricular pacing delays (AV/PV).

Also at step 200, the pacer/ICD senses RV-IEGM and N individual LVn-IEGMsignals along N sensing vectors between the RV tip electrode and each ofthe respective LVn electrodes. The device also detects LVn-QRS eventswithin the LVn-IEGMs and detects RV-QRS events within the RV-IEGM.Exemplary RV and LVn IEGMs are shown in FIG. 4 (in stylized form) for aquadra-pole example wherein the LV lead has four pacing/sensingelectrodes.

More specifically, FIG. 4 illustrates, on its left-hand side, an A-IEGM202 containing a P-wave 204. An RV IEGM 206 includes an RV QRS complex207 triggered by the P-wave via AV conduction. A set of four LV IEGMs208 ₁-208 ₄ are shown. Each includes a version of a single LV QRStriggered by the P-wave via AV conduction, but sensed at slightlydifferent times. The different versions of the LV QRS complex triggeredby the P-wave are denoted 210 ₁-210 ₄. FIG. 4 also illustrates, on itsright-hand side, an A-IEGM 212 containing an A-pulse 214 and resultingatrial evoked response (ER) 215. (The ER may be detected to verifycapture of the atrial pulse and, if necessary, the atrial pulsemagnitude can be increased to compensate for any persistent lack ofcapture.) An RV IEGM 216 includes an RV QRS complex 217 triggered by theA-pulse via AV conduction. A set of four LV IEGMs 218 ₁-218 ₄ are shown.Each includes a version of a single LV QRS triggered by the A-pulse viaAV conduction, but sensed at slightly different times, denoted 220 ₁-220₄. In FIG. 4, the T-wave associated with each QRS is identified by theletter “T”.

Returning to FIG. 3, in response to detection of a P-wave on the A-IEGM,steps 222-226 are performed to measure or otherwise determine variousintrinsic atrioventricular and interventricular intervals. Inparticular, at step 222, the pacer/ICD detects a PR_(RV) intervalbetween the P-wave of the A-IEGM and the RV-QRS of the RV-IEGM. At step224, the device measures Δ_(n) between the RV QRS and each of the N LVnQRS complexes on the N LVn IEGM channels. Note that Δ_(n) values can benegative. If negative, the LV depolarizes first then the RV. Ifpositive, the RV depolarizes first, then the LV.

At step 226, the device then determines PR_(LVn) between the P-wave andeach LVn QRS based on PR_(RV) and the Δ_(n) values by, e.g., calculatingPR_(LVn)=PR_(RV)+Δ_(n). Alternatively, the device could directly measurethe time delays from the P-wave to each LVn QRS. In either case, asingle P-wave can be used to ascertain values for Δ_(n) and PR_(LVn)without needing to perform a separate V sense test for each separate LVelectrode, thus saving time. Due to beat-to-beat variation, preferably asufficient number of P-waves and resulting intervals are detected andmeasured to permit the device to calculate suitable average values. Forexample, a series of P-waves and resulting intervals may be detected andrecorded over a predetermined period of time (such as over one minute)or for a predetermined number of heartbeats (such as at least eightbeats.)

Examples of the various P-wave-triggered interval values determinedduring steps 222-226 are shown in FIG. 4. In these examples, the variousintervals are measured between the start of the P-wave and the peaks ofthe resulting QRS complexes. Other points within these events couldinstead be used in other implementations to measure the intervals.

Within FIG. 3, in response to delivery of an A-pulse, steps 228-232 areperformed to measure or otherwise determine various paced intervals. Inparticular, at step 228, the pacer/ICD detects an AR_(RV) intervalbetween the A-pulse and the RV-QRS of the RV-IEGM. At step 230, thedevice measures Δ_(n) between the RV QRS and each of the N LVn QRScomplexes on the N LVn IEGM channels. At step 232, the device thendetermines AR_(LVn) between the A-pulse and each LVn QRS based onAR_(RV) and the Δ_(n) values by, e.g., calculatingAR_(LVn)=AR_(RV)+Δ_(n). Alternatively, the device could directly measurethe time delays from the A-pulse to each LVn QRS. In either case, asingle A-pulse can be used to ascertain values for Δ_(n) and AR_(LVn)without needing to perform a separate V sense test for each separate LVelectrode, thus saving time. (As with P-waves, although a single A-pulsecan be used to ascertain the various intervals, preferably a sufficientnumber of A-pulse and resulting intervals are detected and measured topermit the device to calculate suitable averages.)

Examples of the various A-pulse-triggered interval values determinedduring steps 228-232 are shown in FIG. 4. In these examples, the variousintervals are measured between the A-pulse and the peaks of theresulting QRS complexes. Other points within these events could insteadbe used in other implementations to measure the intervals.

Continuing with FIG. 3, once intervals have been determined either fromP-waves or from A-pulses, or both, then at step 234 the pacer/ICDperforms a single multi-pole RV pace test to determine IVCD_RLn valuesfor each of the N LV electrodes. This will be described more fully inconnection with FIG. 5. At step 236, the device performs a set of Nmulti-pole LV pace tests to determine IVCD_LRn values for each of the NLV electrodes. This will also be described more fully in connection withFIG. 5. In some embodiments, the device also determines IVCD_L₁R andIVCD_L_(n)L_(m), values, which will be described more fully below withreference to FIGS. 11-14. At step 238, the device determines a set of Ninterventricular correction terms (ε_(n)) from the IVCD_RLn and IVCD_LRnvalues using:

ε_(n)=IVCD_(—) LRn−IVCD_(—) RLn.

At step 240, the pacer/ICD then selects one of the LV electrodes forbiventricular pacing and sets the interventricular pacing delay (VV_(n))for the selected electrode using:

VV _(n)=α_(n)(Δ_(n)+ε_(n))

where α_(n) is 0.5 or other predetermined coefficient. The device thendelivers biventricular pacing using the RV electrode and the selected LVelectrode using the determined VV delay. Alternatively, monoventricularpacing can be delivered by using the sign of Δ_(n) to determine thechamber to pace, i.e. either the RV or the LV.

As to the coefficient α_(n), α_(n) is a programmable or hard-codedparameter that may vary from patient to patient and from electrode toelectrode. In some examples, each of the α_(n) values is set to 0.5,which is a default value. Otherwise routine testing may be employed todetermine preferred or optimal values for α_(n) based, e.g., on anevaluation of the resulting hemodynamics within test patients. Thevalues for α values may differ from electrode to electrode, i.e. α₁ maybe set to a different value than α₂.

The choice of the particular LV electrode for use in pacing may be madebased on various considerations. See, for example, the considerationsset forth in U.S. patent application Ser. No. 11/416,922, of Min et al.,filed May 2, 2006, entitled “System and Method for Determining OptimalPacing Stimulation Sites Based on ECG Information.” Within somepatients, combinations of two or more LV electrodes may be used todeliver ventricular pacing pulses. See, for example, U.S. patentapplication Ser. No. 11/749,662, filed May 16, 2007, of Ryu et al.,entitled “Adaptive Single Site and Multi-Site Ventricular Pacing.” Also,special techniques may be used to perform V sense, RV pace and LV pacetests during atrial fibrillation (AF.) See, for example, U.S. patentapplication Ser. No. 12/507,679, of Min, filed Jul. 22, 2009, andentitled “Systems and Methods for Optimizing Ventricular Pacing Delaysduring Atrial Fibrillation.” That particular document also describestemplate-matching techniques appropriate for use during AF or in anynon-atrial tracking mode, such as VVI.

Where appropriate, the biventricular pacing of step 240 can be used inconjunction with other pacing therapy techniques, such as other CRTtechniques. Briefly, CRT seeks to normalize asynchronous cardiacelectrical activation and resultant asynchronous contractions associatedwith CHF by delivering synchronized pacing stimulus to both ventricles.The stimulus is synchronized so as to improve overall cardiac function.This may have the additional beneficial effect of reducing thesusceptibility to life-threatening tachyarrhythmias.

Thus, FIG. 3 illustrates an exemplary technique for determining anoptimal or preferred value for VV_(n) for each of N LV electrodes. Itshould be understood that these values are not necessarily truly optimalin any particular quantifiable sense. As can be appreciated, whatconstitutes a truly “optimal” value depends on the criteria used forjudging the resulting performance, which can be subjective in the mindsof some clinicians. The values for VV_(n) set at step 240 are,nevertheless, at least preferred values for use in pacing. Cliniciansmay choose to adjust these values via device programming for particularpatients, at their discretion.

Turning now to FIGS. 5-7, techniques for performing RV and LV pace testswill be described. These tests determine values for IVCD_RLn andIVCD_LRn for use in determining the intrinsic interventricularcorrection term (ε_(n)), which is used along with Δ_(n) to set VV_(n)(as already explained.)

For an RV pace test, beginning at step 242 of FIG. 5, the pacer/ICDdelivers an RV pacing pulse using the RV lead (which may include atip/ring electrode pair for delivery of bipolar pulses to the RV). Atstep 244, the pacer/ICD detects resulting LVn QRS complexes on each ofthe N LVn channels. At step 246, the device then measure time delaysbetween the RV pulse and each of the LV QRS complexes detected on the NLVn IEGM channels. At step 248, for each n, the device sets IVCD_RLnbased on the time delays from the RV pulse to LVn QRS.

Exemplary RV and LVn IEGMs are shown in FIG. 6 (in stylized form) for aquadra-pole example of the RV pace test. More specifically, FIG. 6illustrates an RV IEGM 250 that includes an RV evoked response 254triggered by an RV-pulse 252. (The ER may be detected to verify captureof the RV pulse and, if necessary, the RV pulse magnitude can beincreased to compensate for any persistent lack of capture.) A set offour LV IEGMs 256 ₁-256 ₄ are shown. Each includes a version of a singleLV QRS (or an LV “paced propagation”) triggered by the RV-pulse viainterventricular conduction, but sensed at slightly different times. TheLV QRS complexes triggered by the RV-pulse are denoted 258 ₁-258 ₄. TheIVCD_RLn intervals are also shown.

Thus, a single RV-pulse can be used to ascertain values for IVCD_RLnwithout needing to perform a separate RV pace test for each separate LVnelectrode, thus saving time. Although a single RV-pulse can be used toascertain the IVCD_RLn intervals, preferably a sufficient number ofRV-pulses and resulting IVCD_RLn intervals are detected and measured topermit the device to calculate suitable averages.

Returning to FIG. 5, similar steps are performed for an LV pace test,except that a set of N LV pace tests is performed, one test for each ofthe N LV electrodes. Briefly, beginning at step 260, the pacer/ICDdelivers an LV pacing pulse using at least a selected one of the N LVelectrodes of the LV lead. For example, an LV pulse may be delivered ina unipolar configuration between a selected LV electrode (such as“distal” or “tip” electrode LV₁) and the device housing. Alternatively,the pulse may be delivered in a bipolar configuration between any twoadjacent LV electrodes, such as between LV₁ and LV₂, or between LV₂ andLV₃, or between LV₃ and LV₄ (i.e. the proximal LV lead.) These are justsome examples. In general, bipolar pulses may be delivered LVn toLV(n−1) or LV(n+1). Still further, other combinations of LV electrodescan potentially be used to deliver pulses in the bipolar pulseconfiguration, such as LV₁ to LV₄, though adjacent electrode pairs arepreferred. At step 262, the pacer/ICD detects a resulting RV QRS complexon the RV channels as well as paced QRS complexes at all other(non-paced) LV sites. At step 264, the device then measures the timedelay between the LV pulse and the RV QRS complex (or RV pacedpropagation) detected on the RV IEGM channel. At step 266, the devicesets IVCD_LRn based on the time delay from the LV pulse to RV QRScomplex. At step 268, the pacer/ICD then selects another of the LVnelectrodes and repeats steps 260-266 until a value for IVCD_LR has beendetermined for each of the N electrodes of the multi-pole LV lead.

Exemplary RV and LVn IEGMs are shown in FIG. 7 for a quadra-pole exampleof the LV pace test. More specifically, FIG. 7 illustrates a first LVpace test 280 ₁ wherein an LV pulse 272 ₁ is delivered via electrodeLV₁, triggering an LV evoked response 274 ₁ (which may be used to verifycapture.) The LV evoked response is shown on an LV₁ IEGM sensed usingthe LV₁ electrode. The LV pulse also triggers an RV QRS (or RV pacedpropagation) 278 ₁ via interventricular conduction, which is shown on anRV IEGM 276. The IVCD_LR interval between the LV pulse and the RV QRS isshown as IVCD_LR₁. Preferably, a sufficient number of LV-pulses aredelivered and resulting IVCD_RL₁ intervals are measured to permit thedevice to calculate average values of IVCD_LR₁ suitable for use incontrolling VV pacing. It should be understood that, in someembodiments, in addition to detecting the RV QRS as shown, the pacer/ICDcan also detect paced LV QRS complexes at each of the other (non-paced)LV sites and measures various interelectrode IVCD delays between the LVelectrodes (e.g. IVCD_L₁L₂). This is further shown by way of FIG. 14,discussed below. The various interelectrode IVCD delays (e.g.IVCD_L_(n)L_(m)) can be exploited using techniques illustrated in FIGS.11-12, also discussed below.

Similar tests are performed for the other LV electrodes. Briefly, asecond LV pace test 280 ₂ is shown wherein an LV pulse 272 ₂ isdelivered via electrode LV₂, triggering an LV evoked response 274 ₂. TheLV evoked response is shown on an LV₂ IEGM sensed using the LV₂electrode. The LV pulse also triggers an RV QRS 278 ₂ (which is shown onRV IEGM 276) and the IVCD interval IVCD_LR₂ is measured. A third LV pacetest 280 ₃ is shown wherein an LV pulse 272 ₃ is delivered via electrodeLV₃, triggering an LV evoked response 274 ₃. The LV evoked response isshown on an LV₃ IEGM sensed using the LV₃ electrode. The LV pulse alsotriggers an RV QRS 278 ₃ (which is shown on RV IEGM 276) and the IVCDinterval IVCD_LR₃ is measured. A fourth LV pace test 280 ₄ is shownwherein an LV pulse 272 ₄ is delivered via electrode LV₄, triggering anLV evoked response 274 ₄. The LV evoked response is shown on an LV₄ IEGMsensed using the LV₄ electrode. The LV pulse also triggers an RV QRS 278₄ (which is shown on RV IEGM 276) and the IVCD interval IVCD_LR₄ ismeasured. The various RV QRS events occur at slightly different timesrelative to the respective LV pulses and hence the values for IVCD_LRare all slightly different. In any case, these values are recorded andused in step 238 of FIG. 3 to determine values of ε_(n), which are usedas explained above to set VV_(n).

Although primarily described with respect to examples having apacer/ICD, other implantable medical devices may be equipped to exploitthe techniques described herein such as CRT devices and CRT-D devices.For the sake of completeness, an exemplary pacer/ICD will now bedescribed, which includes components for performing the functions andsteps already described.

Exemplary Pacer/ICD

With reference to FIGS. 8 and 9, a description of an exemplary pacer/ICDwill now be provided. FIG. 5 provides a simplified block diagram of thepacer/ICD, which is a dual-chamber stimulation device capable oftreating both fast and slow arrhythmias with stimulation therapy,including cardioversion, defibrillation, and pacing stimulation, andalso capable of setting and using VV pacing delays, as discussed above.To provide other atrial chamber pacing stimulation and sensing,pacer/ICD 10 is shown in electrical communication with a heart 312 byway of a left atrial lead 320 having an atrial tip electrode 322 and anatrial ring electrode 323 implanted in the atrial appendage. Pacer/ICD10 is also in electrical communication with the heart by way of a rightventricular lead 330 having, in this embodiment, a ventricular tipelectrode 332, a right ventricular ring electrode 334, a rightventricular (RV) coil electrode 336, and a superior vena cava (SVC) coilelectrode 338. Typically, the right ventricular lead 330 istransvenously inserted into the heart so as to place the RV coilelectrode 336 in the right ventricular apex, and the SVC coil electrode338 in the superior vena cava. Accordingly, the right ventricular leadis capable of receiving cardiac signals, and delivering stimulation inthe form of pacing and shock therapy to the right ventricle.

To sense left atrial and ventricular cardiac signals and to provide leftchamber pacing therapy, pacer/ICD 10 is coupled to a multi-pole LV lead324 designed for placement in the “CS region” via the CS os forpositioning a distal electrode adjacent to the left ventricle and/oradditional electrode(s) adjacent to the left atrium. As used herein, thephrase “CS region” refers to the venous vasculature of the leftventricle, including any portion of the CS, great cardiac vein, leftmarginal vein, left posterior ventricular vein, middle cardiac vein,and/or small cardiac vein or any other cardiac vein accessible by theCS. Accordingly, an exemplary LV lead 324 is designed to receive atrialand ventricular cardiac signals and to deliver left ventricular pacingtherapy using a set of four left ventricular electrodes 326 ₁, 326 ₂,326 ₃, and 326 ₄ (thereby providing a quadra-pole lead), left atrialpacing therapy using at least a left atrial ring electrode 327, andshocking therapy using at least a left atrial coil electrode 328. The326₁ LV electrode may also be referred to as a “tip” or “distal” LVelectrode. The 326₄ LV electrode may also be referred to as a “proximal”LV electrode. In other examples, more or fewer LV electrodes areprovided. Although only three leads are shown in FIG. 5, it should alsobe understood that additional leads (with one or more pacing, sensingand/or shocking electrodes) might be used and/or additional electrodesmight be provided on the leads already shown, such as additionalelectrodes on the RV lead.

A simplified block diagram of internal components of pacer/ICD 10 isshown in FIG. 9. While a particular pacer/ICD is shown, this is forillustration purposes only, and one of skill in the art could readilyduplicate, eliminate or disable the appropriate circuitry in any desiredcombination to provide a device capable of treating the appropriatechamber(s) with cardioversion, defibrillation and pacing stimulation.The housing 340 for pacer/ICD 10, shown schematically in FIG. 9, isoften referred to as the “can”, “case” or “case electrode” and may beprogrammably selected to act as the return electrode for all “unipolar”modes. The housing 340 may further be used as a return electrode aloneor in combination with one or more of the coil electrodes, 328, 336 and338, for shocking purposes. The housing 340 further includes a connector(not shown) having a plurality of terminals, 342, 343, 344 ₁-344 ₄, 346,348, 352, 354, 356 and 358 (shown schematically and, for convenience,the names of the electrodes to which they are connected are shown nextto the terminals). As such, to achieve right atrial sensing and pacing,the connector includes at least a right atrial tip terminal (A_(R) TIP)342 adapted for connection to the atrial tip electrode 322 and a rightatrial ring (A_(R) RING) electrode 343 adapted for connection to rightatrial ring electrode 323. To achieve left chamber sensing, pacing andshocking, the connector includes a left ventricular tip terminal (VL₁TIP) 344 ₁ and additional LV electrode terminals 344 ₂-344 ₄ for theother LV electrodes of the quadra-pole LV lead.

The connector also includes a left atrial ring terminal (A_(L) RING) 346and a left atrial shocking terminal (A_(L) COIL) 348, which are adaptedfor connection to the left atrial ring electrode 327 and the left atrialcoil electrode 328, respectively. To support right chamber sensing,pacing and shocking, the connector further includes a right ventriculartip terminal (V_(R) TIP) 352, a right ventricular ring terminal (V_(R)RING) 354, a right ventricular shocking terminal (V_(R) COIL) 356, andan SVC shocking terminal (SVC COIL) 358, which are adapted forconnection to the right ventricular tip electrode 332, right ventricularring electrode 334, the V_(R) coil electrode 336, and the SVC coilelectrode 338, respectively.

At the core of pacer/ICD 10 is a programmable microcontroller 360, whichcontrols the various modes of stimulation therapy. As is well known inthe art, the microcontroller 360 (also referred to herein as a controlunit) typically includes a microprocessor, or equivalent controlcircuitry, designed specifically for controlling the delivery ofstimulation therapy and may further include RAM or ROM memory, logic andtiming circuitry, state machine circuitry, and I/O circuitry. Typically,the microcontroller 360 includes the ability to process or monitor inputsignals (data) as controlled by a program code stored in a designatedblock of memory. The details of the design and operation of themicrocontroller 360 are not critical to the invention. Rather, anysuitable microcontroller 360 may be used that carries out the functionsdescribed herein. The use of microprocessor-based control circuits forperforming timing and data analysis functions are well known in the art.

As shown in FIG. 9, an atrial pulse generator 370 and a ventricularpulse generator 372 generate pacing stimulation pulses for delivery bythe right atrial lead 320, the right ventricular lead 330, and/or the LVlead 324 via an electrode configuration switch 374. It is understoodthat in order to provide stimulation therapy in each of the fourchambers of the heart, the atrial and ventricular pulse generators, 370and 372, may include dedicated, independent pulse generators,multiplexed pulse generators or shared pulse generators. The pulsegenerators, 370 and 372, are controlled by the microcontroller 360 viaappropriate control signals, 376 and 378, respectively, to trigger orinhibit the stimulation pulses.

The microcontroller 360 further includes timing control circuitry (notseparately shown) used to control the timing of such stimulation pulses(e.g., pacing rate, AV delay, atrial interconduction (inter-atrial)delay, or ventricular interconduction (V-V) delay, etc.) as well as tokeep track of the timing of refractory periods, blanking intervals,noise detection windows, evoked response windows, alert intervals,marker channel timing, etc., which is well known in the art. Switch 374includes a plurality of switches for connecting the desired electrodesto the appropriate I/O circuits, thereby providing complete electrodeprogrammability. Accordingly, the switch 374, in response to a controlsignal 380 from the microcontroller 360, determines the polarity of thestimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) byselectively closing the appropriate combination of switches (not shown)as is known in the art. The switch also switches among the various LVelectrodes.

Atrial sensing circuits 382 and ventricular sensing circuits 384 mayalso be selectively coupled to the right atrial lead 320, LV lead 324,and the right ventricular lead 330, through the switch 374 for detectingthe presence of cardiac activity in each of the four chambers of theheart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR. SENSE)sensing circuits, 382 and 384, may include dedicated sense amplifiers,multiplexed amplifiers or shared amplifiers. The switch 374 determinesthe “sensing polarity” of the cardiac signal by selectively closing theappropriate switches, as is also known in the art. In this way, theclinician may program the sensing polarity independent of thestimulation polarity. Each sensing circuit, 382 and 384, preferablyemploys one or more low power, precision amplifiers with programmablegain and/or automatic gain control, bandpass filtering, and a thresholddetection circuit, as known in the art, to selectively sense the cardiacsignal of interest. The automatic gain control enables pacer/ICD 10 todeal effectively with the difficult problem of sensing the low amplitudesignal characteristics of atrial or ventricular fibrillation. Theoutputs of the atrial and ventricular sensing circuits, 382 and 384, areconnected to the microcontroller 360 which, in turn, are able to triggeror inhibit the atrial and ventricular pulse generators, 370 and 372,respectively, in a demand fashion in response to the absence or presenceof cardiac activity in the appropriate chambers of the heart.

For arrhythmia detection, pacer/ICD 10 utilizes the atrial andventricular sensing circuits, 382 and 384, to sense cardiac signals todetermine whether a rhythm is physiologic or pathologic. As used in thissection “sensing” is reserved for the noting of an electrical signal,and “detection” is the processing of these sensed signals and noting thepresence of an arrhythmia. The timing intervals between sensed events(e.g., AS, VS, and depolarization signals associated with fibrillationwhich are sometimes referred to as “F-waves” or “Fib-waves”) are thenclassified by the microcontroller 360 by comparing them to a predefinedrate zone limit (i.e., bradycardia, normal, atrial tachycardia, atrialfibrillation, low rate VT, high rate VT, and fibrillation rate zones)and various other characteristics (e.g., sudden onset, stability,physiologic sensors, and morphology, etc.) in order to determine thetype of remedial therapy that is needed (e.g., bradycardia pacing,antitachycardia pacing, cardioversion shocks or defibrillation shocks).

Cardiac signals are also applied to the inputs of an analog-to-digital(ND) data acquisition system 390. The data acquisition system 390 isconfigured to acquire intracardiac electrogram signals, convert the rawanalog data into a digital signal, and store the digital signals forlater processing and/or telemetric transmission to an external device402. The data acquisition system 390 is coupled to the right atrial lead320, the LV lead 324, and the right ventricular lead 330 through theswitch 374 to sample cardiac signals across any pair of desiredelectrodes. The microcontroller 360 is further coupled to a memory 394by a suitable data/address bus 396, wherein the programmable operatingparameters used by the microcontroller 360 are stored and modified, asrequired, in order to customize the operation of pacer/ICD 10 to suitthe needs of a particular patient. Such operating parameters define, forexample, the amplitude or magnitude, pulse duration, electrode polarity,for both pacing pulses and impedance detection pulses as well as pacingrate, sensitivity, arrhythmia detection criteria, and the amplitude,waveshape and vector of each shocking pulse to be delivered to thepatient's heart within each respective tier of therapy. Other pacingparameters include base rate, rest rate and circadian base rate.

Advantageously, the operating parameters of the implantable pacer/ICD 10may be non-invasively programmed into the memory 394 through a telemetrycircuit 400 in telemetric communication with the external device 402,such as a programmer, transtelephonic transceiver or a diagnostic systemanalyzer. The telemetry circuit 400 is activated by the microcontrollerby a control signal 406. The telemetry circuit 400 advantageously allowsintracardiac electrograms and status information relating to theoperation of pacer/ICD 10 (as contained in the microcontroller 360 ormemory 394) to be sent to the external device 402 through an establishedcommunication link 404. Pacer/ICD 10 further includes an accelerometeror other physiologic sensor 408, commonly referred to as a“rate-responsive” sensor because it is typically used to adjust pacingstimulation rate according to the exercise state of the patient.However, the physiological sensor 408 may further be used to detectchanges in cardiac output, changes in the physiological condition of theheart, or diurnal changes in activity (e.g., detecting sleep and wakestates) and to detect arousal from sleep. Accordingly, themicrocontroller 360 responds by adjusting the various pacing parameters(such as rate, AV delay, VV delay, etc.) at which the atrial andventricular pulse generators, 370 and 372, generate stimulation pulses.While shown as being included within pacer/ICD 10, it is to beunderstood that the physiologic sensor 408 may also be external topacer/ICD 10, yet still be implanted within or carried by the patient. Acommon type of rate responsive sensor is an activity sensorincorporating an accelerometer or a piezoelectric crystal, which ismounted within the housing 340 of pacer/ICD 10. Other types ofphysiologic sensors are also known, for example, sensors that sense theoxygen content of blood, respiration rate and/or minute ventilation, pHof blood, ventricular gradient, etc.

The pacer/ICD additionally includes a battery 410, which providesoperating power to all of the circuits shown in FIG. 9. The battery 410may vary depending on the capabilities of pacer/ICD 10. If the systemonly provides low voltage therapy, a lithium iodine or lithium copperfluoride cell typically may be utilized. For pacer/ICD 10, which employsshocking therapy, the battery 410 should be capable of operating at lowcurrent drains for long periods, and then be capable of providinghigh-current pulses (for capacitor charging) when the patient requires ashock pulse. The battery 410 should also have a predictable dischargecharacteristic so that elective replacement time can be detected.Accordingly, appropriate batteries are employed.

As further shown in FIG. 9, pacer/ICD 10 is shown as having an impedancemeasuring circuit 412, which is enabled by the microcontroller 360 via acontrol signal 414. Uses for an impedance measuring circuit include, butare not limited to, lead impedance surveillance during the acute andchronic phases for proper lead positioning or dislodgement; detectingoperable electrodes and automatically switching to an operable pair ifdislodgement occurs; measuring respiration or minute ventilation;measuring thoracic impedance for determining shock thresholds; detectingwhen the device has been implanted; measuring respiration; and detectingthe opening of heart valves, etc. The impedance measuring circuit 412 isadvantageously coupled to the switch 474 so that any desired electrodemay be used.

In the case where pacer/ICD 10 is intended to operate as an implantablecardioverter/defibrillator (ICD) device, it detects the occurrence of anarrhythmia, and automatically applies an appropriate electrical shocktherapy to the heart aimed at terminating the detected arrhythmia. Tothis end, the microcontroller 360 further controls a shocking circuit416 by way of a control signal 418. The shocking circuit 416 generatesshocking pulses of low (up to 0.5 joules), moderate (0.5-10 joules) orhigh energy (11 to 40 joules), as controlled by the microcontroller 360.Such shocking pulses are applied to the heart of the patient through atleast two shocking electrodes, and as shown in this embodiment, selectedfrom the left atrial coil electrode 328, the RV coil electrode 336,and/or the SVC coil electrode 338. The housing 340 may act as an activeelectrode in combination with the RV electrode 336, or as part of asplit electrical vector using the SVC coil electrode 338 or the leftatrial coil electrode 328 (i.e., using the RV electrode as a commonelectrode). Cardioversion shocks are generally considered to be of lowto moderate energy level (so as to minimize pain felt by the patient),and/or synchronized with an R-wave and/or pertaining to the treatment oftachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 7-40joules), delivered asynchronously (since R-waves may be toodisorganized), and pertaining exclusively to the treatment offibrillation. Accordingly, the microcontroller 360 is capable ofcontrolling the synchronous or asynchronous delivery of the shockingpulses.

An internal warning device 399 may be provided for generatingperceptible warning signals to the patient via vibration, voltage orother methods.

Insofar as ventricular pacing is concerned, the microcontroller includesa multi-pole rapid VV optimizer 401 operative to perform or control thetechniques of FIGS. 2-7, described above. The optimizer includes aP-wave/A-pulse unit 403 operative to identify electrical eventssufficient to trigger ventricular depolarization within the heart of thepatient. A multi-pole LVn QRS detection unit 405 is operative to detecta resulting ventricular depolarization at each of a plurality ofelectrodes of the multi-pole LV lead. The RV QRS is detected by othercomponents of the device.

A multi-pole intrinsic interventricular conduction time delay (An)determination unit 407 is operative to determine an interventricularconduction time delay for each of the electrodes of the multi-pole leadbased on the depolarization triggered by A-pulses/P-waves, theconduction time delay including a paced interventricular conduction timedelay and/or an intrinsic interventricular conduction time delay.

A multi-pole RV paced interventricular conduction time delay (IVCD_RLn)determination unit 409 controls RV pace tests to determine values forIVCD_RLn. A multi-pole LV paced interventricular conduction time delay(IVCD_LRn) determination unit 411 controls LV pace tests to determinevalues for IVCD_LRn. A multi-pole pacing controller 413 is operative tocontrol ventricular pacing using a selected electrode of the multi-poleLV lead based on interventricular conduction time delays determined forthat electrode during the V sense, RV pace and LV pace tests.

In addition to performing technique described above, the pacer/ICD ofFIG. 9 can also perform the various techniques described below withreference to FIGS. 11-14. In particular, rapid optimizer 401 can performof control the techniques of FIGS. 11-14. To this end, the rapidoptimizer may include a summation-based LV site sorting unit 415(operative to perform the techniques of FIG. 14, discussed below) and ashort PV/AV delay identification and correction unit 417 (operative toperform the short PV/AV techniques of FIG. 12, also discussed below.)

Depending upon the implementation, the various components of themicrocontroller may be implemented as separate software modules or themodules may be combined to permit a single module to perform multiplefunctions. In addition, although shown as being components of themicrocontroller, some or all of these components may be implementedseparately from the microcontroller, using application specificintegrated circuits (ASICs) or the like.

As noted, at least some of the techniques described herein can beperformed by (or under the control of) an external device. For the sakeof completeness, an exemplary device programmer will now be described,which includes components for controlling at least some of the functionsand steps already described.

Exemplary External Programmer

FIG. 10 illustrates pertinent components of an external programmer 14for use in programming the pacer/ICD of FIG. 9 and for performing theabove-described optimization techniques. For the sake of completeness,other device programming functions are also described herein. Generally,the programmer permits a physician or other user to program theoperation of the implanted device and to retrieve and displayinformation received from the implanted device such as IEGM data anddevice diagnostic data. Additionally, the external programmer can beoptionally equipped to receive and display electrocardiogram (EKG) datafrom separate external EKG leads that may be attached to the patient.Depending upon the specific programming of the external programmer,programmer 14 may also be capable of processing and analyzing datareceived from the implanted device and from the EKG leads to, forexample, render preliminary diagnosis as to medical conditions of thepatient or to the operations of the implanted device.

Now, considering the components of programmer 14, operations of theprogrammer are controlled by a CPU 502, which may be a generallyprogrammable microprocessor or microcontroller or may be a dedicatedprocessing device such as an application specific integrated circuit(ASIC) or the like. Software instructions to be performed by the CPU areaccessed via an internal bus 504 from a read only memory (ROM) 506 andrandom access memory 530. Additional software may be accessed from ahard drive 508, floppy drive 510, and CD ROM drive 512, or othersuitable permanent mass storage device. Depending upon the specificimplementation, a basic input output system (BIOS) is retrieved from theROM by CPU at power up. Based upon instructions provided in the BIOS,the CPU “boots up” the overall system in accordance withwell-established computer processing techniques.

Once operating, the CPU displays a menu of programming options to theuser via an LCD display 514 or other suitable computer display device.To this end, the CPU may, for example, display a menu of specificprogrammable parameters of the implanted device to be programmed or maydisplay a menu of types of diagnostic data to be retrieved anddisplayed. In response thereto, the physician enters various commandsvia either a touch screen 516 overlaid on the LCD display or through astandard keyboard 518 supplemented by additional custom keys 520, suchas an emergency VVI (EVVI) key. The EVVI key sets the implanted deviceto a safe VVI mode with high pacing outputs. This ensures lifesustaining pacing operation in nearly all situations but by no means isit desirable to leave the implantable device in the EVVI mode at alltimes.

Once all pacing leads are mounted and the pacing device is implanted,the various parameters are programmed. Typically, the physicianinitially controls the programmer 14 to retrieve data stored within anyimplanted devices and to also retrieve EKG data from EKG leads, if any,coupled to the patient. To this end, CPU 502 transmits appropriatesignals to a telemetry subsystem 522, which provides components fordirectly interfacing with the implanted devices, and the EKG leads.Telemetry subsystem 522 includes its own separate CPU 524 forcoordinating the operations of the telemetry subsystem. Main CPU 502 ofprogrammer communicates with telemetry subsystem CPU 524 via internalbus 504. Telemetry subsystem additionally includes a telemetry circuit526 connected to telemetry wand 528, which, in turn, receives andtransmits signals electromagnetically from a telemetry unit of theimplanted device. The telemetry wand is placed over the chest of thepatient near the implanted device to permit reliable transmission ofdata between the telemetry wand and the implanted device. Herein, thetelemetry subsystem is shown as also including an EKG circuit 534 forreceiving surface EKG signals from a surface EKG system 532. In otherimplementations, the EKG circuit is not regarded as a portion of thetelemetry subsystem but is regarded as a separate component.

Typically, at the beginning of the programming session, the externalprogramming device controls the implanted devices via appropriatesignals generated by the telemetry wand to output all previouslyrecorded patient and device diagnostic information. Patient diagnosticinformation includes, for example, recorded IEGM data and statisticalpatient data such as the percentage of paced versus sensed heartbeats.Device diagnostic data includes, for example, information representativeof the operation of the implanted device such as lead impedances,battery voltages, battery recommended replacement time (RRT) informationand the like. Data retrieved from the pacer/ICD also includes the datastored within the recalibration database of the pacer/ICD (assuming thepacer/ICD is equipped to store that data.) Data retrieved from theimplanted devices is stored by external programmer 14 either within arandom access memory (RAM) 530, hard drive 508 or within a floppydiskette placed within floppy drive 510. Additionally, or in thealternative, data may be permanently or semi-permanently stored within acompact disk (CD) or other digital media disk, if the overall system isconfigured with a drive for recording data onto digital media disks,such as a write once read many (WORM) drive.

Once all patient and device diagnostic data previously stored within theimplanted devices is transferred to programmer 14, the implanted devicesmay be further controlled to transmit additional data in real time as itis detected by the implanted devices, such as additional IEGM data, leadimpedance data, and the like. Additionally, or in the alternative,telemetry subsystem 522 receives EKG signals from EKG leads 532 via anEKG processing circuit 534. As with data retrieved from the implanteddevice itself, signals received from the EKG leads are stored within oneor more of the storage devices of the external programmer. Typically,EKG leads output analog electrical signals representative of the EKG.Accordingly, EKG circuit 534 includes analog to digital conversioncircuitry for converting the signals to digital data appropriate forfurther processing within the programmer. Depending upon theimplementation, the EKG circuit may be configured to convert the analogsignals into event record data for ease of processing along with theevent record data retrieved from the implanted device. Typically,signals received from the EKG leads are received and processed in realtime.

Thus, the programmer receives data both from the implanted devices andfrom optional external EKG leads. Data retrieved from the implanteddevices includes parameters representative of the current programmingstate of the implanted devices. Under the control of the physician, theexternal programmer displays the current programmable parameters andpermits the physician to reprogram the parameters. To this end, thephysician enters appropriate commands via any of the aforementionedinput devices and, under control of CPU 502, the programming commandsare converted to specific programmable parameters for transmission tothe implanted devices via telemetry wand 528 to thereby reprogram theimplanted devices. Prior to reprogramming specific parameters, thephysician may control the external programmer to display any or all ofthe data retrieved from the implanted devices or from the EKG leads,including displays of EKGs, IEGMs, and statistical patient information.Any or all of the information displayed by programmer may also beprinted using a printer 536.

Additionally, CPU 502 also preferably includes an interval-based rapidVV optimizer 550 operative to perform or control the techniques of FIGS.2-7, described above. CPU 502 also preferably includes a multi-polerapid ventricular VV optimizer 550 and a multi-pole pacing controlleroperative to perform or control the techniques of FIGS. 2-7, describedabove. These components operate to analyze data received from thepacer/ICD, such as LVn-IEGM and RV-IEGM data, and to determine optimalor preferred VV_(n) pacing delays for use in biventricular pacing or todetermine the optimal ventricular chambers for use in monoventricularpacing. Pacing delay parameters and/or other pacing control informationmay then be transmitted to the pacer/ICD under the control the pacingcontroller to program the device to perform pacing in accordance withthe optimal or preferred VV_(n) pacing delays or in accordance with anymonoventricular pacing control parameters.

In addition to performing technique described above, the system of FIG.10 can also control or perform the various techniques described belowwith reference to FIGS. 11-14. In particular, rapid optimizer 550 canperform of control the techniques of FIGS. 11-14 based on data or othersignals received from a pacer/ICD. To this end, the rapid optimizer mayinclude a summation-based LV site sorting unit 554 (operative to controlor perform the techniques of FIG. 14, discussed below) and a short PV/AVdelay identification and correction unit 556 (operative to perform theshort PV/AV techniques of FIG. 12, also discussed below.)

Programmer/monitor 14 also includes a modem 538 to permit directtransmission of data to other programmers via the public switchedtelephone network (PSTN) or other interconnection line, such as a T1line or fiber optic cable. Depending upon the implementation, the modemmay be connected directly to internal bus 504 may be connected to theinternal bus via either a parallel port 540 or a serial port 542. Otherperipheral devices may be connected to the external programmer viaparallel port 540 or a serial port 542 as well. Although one of each isshown, a plurality of input output (IO) ports might be provided. Aspeaker 544 is included for providing audible tones to the user, such asa warning beep in the event improper input is provided by the physician.Telemetry subsystem 522 additionally includes an analog output circuit545 for controlling the transmission of analog output signals, such asIEGM signals output to an EKG machine or chart recorder.

With the programmer configured as shown, a physician or other useroperating the external programmer is capable of retrieving, processingand displaying a wide range of information received from the implanteddevice and to reprogram the implanted device if needed. The descriptionsprovided herein with respect to FIG. 10 are intended merely to providean overview of the operation of programmer and are not intended todescribe in detail every feature of the hardware and software of theprogrammer and is not intended to provide an exhaustive list of thefunctions performed by the programmer.

In the following additional and/or alternative techniques are describedwherein the order by which LV sites are paced is sorted and optimizedand wherein circumstances where AV/PV pacing delays are longer thancorresponding AR/PR conduction delays are addressed.

Additional Multi-Pole LV Pacing Optimization Techniques

FIG. 11 broadly summarizes an alternative technique for controllingventricular pacing for use with a multi-pole ventricular lead that maybe exploited by the pacer/ICD of FIG. 1 or other suitably equippedsystems. Beginning at step 600, the pacer/ICD determines preliminarymulti-site interventricular pacing time delays (VVT) for each of a setof electrodes of a multi-polar lead based on multi-site interventricularconduction time delay values (Δ) determined for the electrodes. At step602, the device determines multi-site interelectrode pacing delays (IVV)for the electrodes of the multi-pole lead based the preliminaryinterventricular pacing delays (VVT). In one example described below,the IVV values are derived from the preliminary VVT values using aparticular summation technique that iteratively sums the variousinterelectrode delays. At step 604, the device determines the preferredor optimal order by which the electrodes of the multi-pole lead are tobe used to deliver multi-site pacing pulses, with the order determinedbased on the interelectrode pacing time delays (IVV) using techniques tobe described below. For the example of MSLV pacing, the pacer/ICDdetermines the order by which a set of MSLV pulses are to be deliveredusing the electrodes of the multi-pole LV lead. At step 606, the devicethen delivers multi-site ventricular pacing by delivering (orcontrolling the delivery of) a set of pulses using the electrodes of themulti-pole lead in the order determined at step 604. As will beexplained, the pulses are delivered subject to a set of finalinterventricular pacing delays (W), which are derived from IVV values.Note that these multi-site stimulation pulses are typically delivered inthe sorted sequence during a single cardiac cycle. These techniques willbe described in more detail with reference to the remaining figures.

FIG. 12 provides a more detailed example wherein MSLV pacing iscontrolled for use with a multi-pole LV lead having N electrodes(individually denoted LV_(n) where n=0 . . . N−1). Note that some of theinitial steps of FIG. 12 are the same or similar to those of FIG. 3,discussed above and will not be described again in detail. Beginning atstep 700, the pacer/ICD performs a single V sense test. As explainedabove, during the V sense test, the pacer/ICD: detects P-waves on anA-IEGM channel sensed using an RA lead and/or delivers A-pulse to the RAusing the RA lead. Also at step 700, the pacer/ICD senses RV-IEGM and Nindividual LV_(n)-IEGM signals along N sensing vectors between the RVtip electrode and each of the respective LV_(n) electrodes. The devicealso detects LV_(n)-QRS events within the LV_(n)-IEGMs and detectsRV-QRS events within the RV-IEGM. Exemplary RV and LV_(n) IEGMs areshown in FIG. 4, discussed above.

In response to detection of a P-wave on the A-IEGM, steps 722-726 areperformed to measure or otherwise determine various intrinsicatrioventricular and interventricular intervals. In particular, at step722, the pacer/ICD detects a PR_(RV) interval between the P-wave of theA-IEGM and the RV-QRS of the RV-IEGM. At step 724, the device measuresintrinsic interventricular conduction delays (Δ_(n)) between the RV QRSand each corresponding LV_(n) QRS complex on the N LV_(n) IEGM channels.Note that Δ_(n) values can be negative. If negative, the LV depolarizesfirst then the RV. If positive, the RV depolarizes first, then the LV.

At step 725, the device determines interelectrode delays (Δ′_(n)) fromthe interventricular conduction delays (Δ_(n)) based on:

Δ′_(n)=Δ_(n)−Δ_(n−1); where n=2, 3, . . . , N

Δ′₁=Δ₁

wherein Δ_(n) is the measured intrinsic interventricular conduction timedelay for the nth electrode of the multi-pole lead.

At step 726, the device then determines PR_(LVn) between the P-wave andeach LV_(n) QRS based on PR_(RV) and the Δ_(n) values by, e.g.,calculating PR_(LVn)=PR_(RV)+Δ_(n). Note that a single P-wave can beused to ascertain values for Δ_(n) and PR_(LVn) without needing toperform a separate V sense test for each separate LV electrode, thussaving time.

Examples of the various P-wave-triggered interval values determinedduring steps 722-726 are also shown in FIG. 4. In the examples, thevarious intervals are measured between the start of the P-wave and thepeaks of the resulting QRS complexes. Other points within these eventscould instead be used in other implementations to measure the intervals.

Within FIG. 12, in response to delivery of an A-pulse, steps 728-732 areperformed to measure or otherwise determine various paced intervals. Inparticular, at step 728, the pacer/ICD detects an AR_(RV) intervalbetween the A-pulse and the RV-QRS of the RV-IEGM. At step 730, thedevice measures Δ_(n) between the RV QRS and each of the N LVn QRScomplexes on the N LVn IEGM channels.

At step 731, the device determines interelectrode delays (Δ′_(n)) valuesbased on:

Δ′_(n)=Δ_(n)−Δ_(n−1); where n=2, 3, . . . , N

Δ′₁=Δ₁

wherein Δ_(n) is again the measured intrinsic interventricularconduction time delay for the nth electrode of the multi-pole lead.

At step 732, the device then determines AR_(LVn) between the A-pulse andeach LVn QRS based on AR_(RV) and the Δ_(n) values by, e.g., calculatingAR_(LVn)=AR_(RV)+Δ_(n). A single A-pulse can be used to ascertain valuesfor Δ_(n) and AR_(LVn) without needing to perform a separate V sensetest for each separate LV electrode, thus saving time.

Examples of various A-pulse-triggered interval values measured duringsteps 728-732 are shown in FIG. 4. In these examples, the variousintervals are measured between the A-pulse and the peaks of theresulting QRS complexes. Other points within these events could insteadbe used in other implementations to measure the intervals.

Continuing with FIG. 12, once intervals have been determined either fromP-waves or from A-pulses, or both, then at step 734 the pacer/ICDperforms a single multi-pole RV pace test to determine IVCD_RL_(n)values for each of the N LV electrodes. This was described more fullyabove in connection with FIG. 5. At step 736, the device performs a setof N multi-pole LV pace tests to determine IVCD_LRn values for each ofthe N LV electrodes. This was described in connection with FIG. 5. See,also, FIG. 13, which more clearly shows that, for each of the LV pacetests, the pacer/ICD measures an entire set of interelectrode delays.

In FIG. 13, a first graph 737 illustrates an V sense IEGM sensed usingthe RV electrode (in a unipolar configuration, i.e. RV tip-to-can). Aset of graphs 738 ₁-738 ₄ illustrate IEGMs sensed using the various LVelectrodes (again in unipolar configuration.) In this particularexample, a pacing pulse or spike 740 is applied using the second LVelectrode, trigger an evoked response 742 at the site of the second LVelectrode and a set of paced QRS complexes 744 ₁, 744 ₃, and 744 ₄ atthe other LV sites (as well as a paced QRS 746 in the RV.) Various IVCDvalues are measured from the time of the pacing pulse at the variouspaced QRS complexes, including IVCD_L₂R, IVCD_L₂L₁, IVCD_L₂L₃, andIVCD_L₂L₄, as shown.

Additionally, for the quadra-pole example, three other LV pace tests areperformed by delivering LV pulses to the other LV electrodes. Forexample, an LV pulse is delivered using the LV₁ electrode so as totrigger paced QRS's at the other LV sites to allow measurement ofcorresponding IVCD values between the LV₁ electrode and the other sites(IVCD_L₁R, IVCD_L₁L₂, IVCD_L₁L₃, and IVCD_L₁L₄.) Likewise, pulses aredelivered at LV₃ and LV₄ to detect still other IVCD values.

Returning to FIG. 12, at step 748, the device determines a set of Ninterventricular correction terms (ε_(n)) from the IVCD values using:

ε_(n)=IVCD(L _(n) L _(n−1))−IVCD(L _(n−1) L _(n)) where n=2, 3, . . . ,N

ε₁=IVCD(L ₁ R)−IVCD(RL ₁)

wherein IVCD represents the paced interventricular conduction time delay(IVCD) for various pairs of electrodes of the system as determined usingRV pace and LV pace tests and N is the number of electrodes.

At step 750, the pacer/ICD then selects a set of LV electrodes for MSLVpacing and sets the interventricular pacing delays (VVT_(n)) for theelectrodes using:

VVT _(n)=α_(n)(Δ′_(n)+ε_(n)); n=1, 2, . . . , N

where α_(n) is 0.5 or other predetermined coefficient. As noted above,α_(n) is a programmable or hard-coded parameter that may vary frompatient to patient and from electrode to electrode. The vales for α_(n)for use with step 750 of FIG. 12 may differ from those used inconnection with the techniques discussed above. At step 752, thepacer/ICD then determines the order by which the LV sites are to bepaced during MSLV pacing based on VVT_(n). One technique for determiningthe order of MSLV pacing is shown in FIG. 14.

At step 754 of FIG. 14, the pacer/ICD determine a set of interelectrodeVV (IVV) values by summing:

Sum=0

IVV(0)=0 (for RV electrode)

For i=1 to N

-   -   Sum=Sum+VVT(i);    -   IVV(i)=Sum;

End loop.

As such, for the quadra-pole example:

IVV(1)=VVT(1)

IVV(2)=VVT(1)+VVT(2)

IVV(3)=VVT(1)+VVT(2)+VVT(2)

IVV(4)=VVT(1)+VVT(2)+VVT(3)+VVT(4).

Then, at step 756, the pacer/ICD sorts the IVV(n) values in descendingor ascending order by IVV(n) values using the RV as the origin (i.e. 0)by:

-   -   finding the max (IVV(n); i=0, 1, 2, . . . , N);    -   inserting the IVV value into a 2×N sorting array as item        sort(1,1) with the corresponding n value inserted as sort(1,2)    -   removing this entry from IVV(n) and continuing to find the max        IVV with from among the remaining values to fill the array so as        to store the descending order of IVV values in the sort array        with corresponding electrode index number. [Note that, if min is        instead used in sorting instead of max, ascending order is        generated instead of descending order.]

Then, at step 757, the device sets the VV delays for each site based onthe sorted order of sites by applying IVV values as follows (wheresort(n,1) stores IVV values and sort(n,2) stores the order of LVelectrode):

-   -   the 1st V site to be paced is sort(1,2) with AV delay as        determined and VV[1]=0;    -   the 2nd V site to be paced is sort(2,2) with VV[2] delay of        (sort(1,1)−sort(2,1))    -   the 3rd V site to be paced is sort(3,2) with VV[3] delay of        (sort(2,1)−sort(3,1))    -   the 4th V site to be paced is sort(4,2) with VV[4] delay of        (sort(3,1)−sort(4,1)); and    -   the 5th V site to be paced is sort(5,2) with VV[5] delay of        (sort(4,1)−sort(5,1))        and where:

VV[1]=0;

VV[2]=(sort(1,1)−sort(2,1))

VV[3]=(sort(2,1)−sort(3,1))

VV[4]=(sort(3,1)−sort(4,1))

VV[5]=(sort(4,1)−sort(5,1)).

Thus, using this technique, the device finds the max of absolute(IVV_(n))=max (IVV). The site with max IVV is the site to be paced firstwith the PV and AV delays from the formula set forth below. IVV issorted in descending (or, alternatively, in ascending order) by IVV(n)values with RV as origin (i.e. RV=0.) In one particular example, theorder with which stimulation pulses are to be delivered to the fourelectrodes of the LV lead is: 3rd electrode, 1st electrode, 2ndelectrode and 4th electrode, with the RV electrode paced last. That is,the sorted order is: IVV(3), IVV(1), IVV(2), IVV(4), RV=0. In thatexample, the VV delay applied at the 3rd electrode (VV₃) is IVV(3); theVV delay applied at the 1st electrode (VV₁) is: IVV(3)-IVV(1); the VVdelay applied at the 2nd electrode (VV₂) electrode is: IVV(1)-IVV(2);the VV delay applied at the 4th electrode (VV₄) electrode isIVV(2)-IVV(4); and the delay applied to the RV electrode is IVV(4)-0.

Returning to FIG. 12, at step 758 the device then determines if the VVTvalues result in PV and AV values that are sufficiently short. That is,for the LV sites to be paced, the device verifies that PV<PR and AV<ARfor each of the LV sites and, if not, the device identify alternativesites where:

for PR/PV:

-   -   for the 1st V site to be paced (sort(1,2)): PV<PR (at 1^(st)        site or sort(1,2))    -   for the 2nd V site to be paced (sort(2,2)): PV+VV[2]<PR (at        2^(nd) site or sort(2,2))    -   for the 3rd V site to be paced (sort(3,2)): PV+VV[2] VV[3]<PR        (at 3^(rd) site or sort(3,2))    -   for the 4th V site to be paced (sort(4,2)):        PV+VV[2]+VV[3]+VV[4]<PR (at 4^(th) site or sort(4,2))    -   for the 5th V site to be paced (sort(5,2)):        PV+VV[2]+VV[3]+VV[4]+VV[5]<PR (at 5^(th) site or sort(5,2)) and

for AR/AV:

-   -   for the 1st V site to be paced (sort(1,2)): AV<AR (at 1^(st)        site or sort(1,2))    -   for the 2nd V site to be paced (sort(2,2)): AV+VV[2]<AR (at        2^(nd) site or sort(2,2))    -   for the 3rd V site to be paced (sort(3,2)): AV+VV[2] VV[3]<AR        (at 3^(rd) site or sort(3,2))    -   for the 4th V site to be paced (sort(4,2)):        AV+VV[2]+VV[3]+VV[4]<AR (at 4^(th) site or sort(4,2))    -   for the 5th V site to be paced (sort(5,2)):        AV+VV[2]+VV[3]+VV[4]+VV[5]<AR (at 5^(th) site or sort(5,2))        and then select one of those alternate LV electrode sites. The        device then selects one of those alternate LV electrode sites        (and the LV electrodes corresponding to those sites) for pacing.        These alternative sites are to be paced without RV pacing. That        is, all MSLV pacing will be LV only, with no pacing delivered        using the RV.

At step 760, the device then delivers a set of MSLV pacing pulsesbetween the selected pairs of electrodes while cycling through the LVelectrodes corresponding to the selected sites in the sorted order (asdetermined at step 752) and while applying the VV_(n) values as finalinterventricular pacing delay (as determined at step 757 of FIG. 14) andwhile also using alternate sites, if needed, as indicated at step 758.Where appropriate, the MSLV pacing of step 760 can be used inconjunction with other pacing therapy techniques, such as other CRTtechniques.

Thus, FIG. 12 illustrates exemplary techniques for determining optimalor preferred values for VV_(n) for a set of N LV electrodes for use inMSLV pacing. It should again be understood that these values are notnecessarily truly optimal in any particular quantifiable sense. As canbe appreciated, what constitutes a truly optimal value depends on thecriteria used for judging the resulting performance, which can besubjective in the minds of some clinicians. The values for VV_(n) usedat step 760 are, nevertheless, at least preferred values for use inpacing. Clinicians may choose to adjust these values via deviceprogramming for particular patients, at their discretion.

In general, while the invention has been described with reference toparticular embodiments, modifications can be made thereto withoutdeparting from the scope of the invention. Note also that the term“including” as used herein is intended to be inclusive, i.e. “includingbut not limited to.”

1. A method for controlling multi-site ventricular pacing for use by animplantable cardiac rhythm management device equipped with a multi-poleventricular lead having a plurality of electrodes, the methodcomprising: determining preliminary multi-site interventricular pacingdelays (VVT) for the plurality of electrodes of the multi-pole leadbased, at least in part, on multi-site interventricular conduction timedelay values (Δ) determined for the electrodes; determining multi-siteinterelectrode pacing delays (IVV) for the plurality of electrodes ofthe multi-pole lead based the preliminary interventricular pacing delays(VVT); determining an order by which the electrodes of the multi-polelead are to be used to deliver a set of multi-site pacing pulses, withthe order determined based on the interelectrode pacing time delays(IVV); and delivering multi-site ventricular pacing by delivering a setof pulses using the electrodes of the multi-pole lead in the determinedorder.
 2. The method of claim 1 wherein the multi-pole lead is a leftventricular (LV) lead having a plurality of electrodes (LV_(n)) and thedevice is equipped with a right ventricular (RV) lead and wherein themethod is performed to deliver multi-site LV (MSLV) pacing using theplurality of electrodes (LV_(n)) of the multi-pole LV lead, where n=1,
 2. . . , N.
 3. The method of claim 2 wherein determining the preliminaryinterventricular pacing delays (VVT) includes setting an individualpreliminary interventricular pacing delay (VVT_(n)) for use with aselected electrode (LV_(n)) of the LV lead based on:VVT _(n)=α*(Δ′_(n)+ε_(n)); wherein α_(n) is a coefficient, Δ′_(n) is anintrinsic interelectrode conduction time delay, ε_(n) is aninterventricular correction term for use with the selected electrode(LV_(n)) of the LV lead and N represents the total number of electrodesof the multi-pole lead.
 4. The method of claim 3 wherein the intrinsicinterelectrode conduction time delays (Δ′_(n)) are determined using:Δ′_(n)=Δ_(n)−Δ_(n−1); where n=2, 3, . . . , NΔ′₁=Δ₁ wherein Δ_(n) is a measured intrinsic interventricular conductiontime delay for the nth electrode of the multi-pole lead.
 5. The methodof claim 4 wherein the interventricular correction term (ε_(n)) isdetermined based on:ε_(n)=IVCD(L _(n) L _(n−1))−IVCD(L _(n−1) L _(n)) where n=2, 3, . . . ,Nε₁=IVCD(L ₁ R)−IVCD(RL ₁) wherein each value of IVCD represents a pacedinterventricular conduction time delay (IVCD).
 6. The method of claim 3wherein determining multi-site interelectrode pacing delays (IVV) forthe plurality of electrodes based the preliminary interventricularpacing delays (VVT) includes: sequentially summing values of VVT_(n) togenerate corresponding values for IVV_(n).
 7. The method of claim 6wherein determining an order by which the electrodes of the multi-polelead are to be used to deliver a set of multi-site pacing pulses:determining absolute values of each of the IVV_(n) values; identifying aparticular IVV_(n) value having a maximum absolute value and thenselecting the corresponding electrode as being a first electrode to beused for delivering MSLV pacing; and repeating the process with theremaining IVV_(n) values and the remaining electrodes to iterativelysort the IVV_(n) values and the corresponding electrodes.
 8. The methodof claim 7 wherein delivering multi-site ventricular pacing includes:determining final interventricular pacing delays (VV_(n)) for use witheach of the electrodes of the LV lead based on differences betweenIVV_(n) values of the electrodes; delivering a first MSLV pulse usingthe first selected electrode; and delivering additional MSLV pulsesusing the other electrodes of the multi-pole lead in the sorted orderand subject to the final interventricular pacing delays VV_(n).
 9. Themethod of claim 8 further including a predecessor step of determiningmulti-site interventricular conduction time delay values (Δ) for theelectrodes of the LV lead by: identifying an electrical event sufficientto trigger ventricular depolarization within the heart of a patient inwhich the device is implanted; detecting a resulting ventriculardepolarization at each of a plurality of electrodes of the LV lead, thedepolarization being detected at generally different times at eachdifferent electrode; and determining multi-site interventricularconduction time delays (Δ_(n)) for each of the plurality of electrodesof the LV lead based on the depolarization triggered by the electricalevent.
 10. The method of claim 9 wherein detecting the resultingventricular depolarization at each of a plurality of electrodes of theLV lead includes detecting a resulting LV QRS complex (LV_(n) QRS) ateach of the plurality of LV electrodes (LV_(n)) of the LV lead.
 11. Themethod of claim 1 wherein all of the steps are performed by theimplantable medical device.
 12. The method of claim 1 wherein at leastsome of the steps are performed by an external device based on signalsreceived from the implantable medical device.
 13. A system forcontrolling ventricular pacing for use by an implantable cardiac rhythmmanagement device equipped with a multi-pole ventricular lead having aplurality of electrodes, the system comprising: a multi-siteinterventricular pacing delay determination unit operative to determinepreliminary multi-site interventricular pacing delays (VVT) for theplurality of electrodes of the multi-pole lead based, at least in part,on multi-site interventricular conduction time delay values (Δ)determined for the electrodes; a multi-site interelectrode pacing delaydetermination unit operative to determine multi-site interelectrodepacing delays (IVV) for the plurality of electrodes of the multi-polelead based the preliminary interventricular pacing delays (VVT); amulti-pole pacing site ordering unit operative to determine an order bywhich the electrodes of the multi-pole lead are to be used to deliver aset of multi-site pacing pulses, with the order determined based on theinterelectrode pacing time delays (IVV); and a multi-pole ventricularpacing controller operative to deliver a set of pulses using theelectrodes of the multi-pole lead.
 14. A system for controllingventricular pacing for use by an implantable cardiac rhythm managementdevice equipped with a multi-pole ventricular lead having a plurality ofelectrodes, the system comprising: means for determining preliminarymulti-site interventricular pacing delays (VVT) for the plurality ofelectrodes of the multi-pole lead based, at least in part, on multi-siteinterventricular conduction time delay values (Δ) determined for theelectrodes; means for determining multi-site interelectrode pacingdelays (IVV) for the plurality of electrodes of the multi-pole leadbased the preliminary interventricular pacing delays (VVT); means fordetermining an order by which the electrodes of the multi-pole lead areto be used to deliver a set of multi-site pacing pulses, with the orderdetermined based on the interelectrode pacing time delays (IVV); andmeans for delivering multi-site ventricular pacing by delivering a setof pulses using the electrodes of the multi-pole lead.